Method for depositing thin layers of a material consisting of chemical compounds comprising a metal from group IV of the periodic system, nitrogen and oxygen onto heatable substrates

ABSTRACT

The invention concerns process for producing thin layers of a material containing chemical compounds between a metal from group IV A of the periodic system, nitrogen and oxygen. The optical and electrical properties of this material can be set within wide limits by means of small voids, without the need to alter the chemical composition. The material is suitable in particular for use as a selective radiation converter in the solar energy and power industry. Aside from other processes for its manufacture, it can be produced as a thin coating deposited on a substrate by means of reactive evaporation.

CONTINUATION STATEMENT

The present application is a division of patent application Ser. No.08/276,026, filed 15 Jul. 1994, now U.S. Pat. No. 5,670,248.

BACKGROUND OF THE INVENTION

The invention concerns a material composed of a metal from group IV ofthe periodic chart, nitrogen and oxygen having the formula MN_(x) O_(y)wherein M is a metal from group IV, _(x) and _(y) range from about 0.1to 1.7 and wherein 2 to 45% of the volume is comprised of voids rangingfrom (0.5 nm)³ to about (100 nm)³ in size. This material can be used toconvert radiation energy to heat energy, serve as an anti-reflectivelayer, radiation emitter or antimicrobial agent. It is preferablymanufactured by a vacuum deposition technique. Further, the inventionrelates generally to chemical compositions containing metals from groupIV of the periodic chart, nitrogen, and oxygen and having voidsdistributed within such composition.

Compounds of titanium with nitrogen and oxygen cover a broad range ofthe known properties of substances and are therefore widely used inindustry. Titanium dioxide, for example, is a principal component ofpaints for walls, but is also used in solar cells. The compound TiN isknown as an electrically conductive ceramic and distinguished by highresistance and hardness. Tools are hardened with it, and this compoundis utilized in the semiconductor industry as a diffusion barrier betweensilicon and aluminum. Mixtures of TiN and titanium oxide phases have notbeen thoroughly studied. For practical applications, materials combiningthe two properties, dielectric and metallic, would be very attractive.

The authors of Offenlegungsschrift DE-OS 3,522,427 A1 disclose amaterial comprising titanium and nitrogen whose electrical proper-tiesare adapted to various applications by the admixture of oxygen. Thisleads to changes in the chemical composition and has a negativeinfluence upon other physical and chemical properties, for example,adhesiveness, resistance to corrosion, resistance to temperature orhardness. Particularly detrimental thereby is the fact that thismaterial tends to oxidize when it is exposed to oxygen. But because thedesired properties are determined by the portion of oxygen, they changewith time, which stands in the way of practical application.

In the US patent specification of Blickensderfer, et al., U.S. Pat. No.4,098,956, a selective absorber is disclosed, which is coated withTiN_(x) O_(y). The patentees report on the presence of oxygen and carbonin the coating. Voids or empty spaces, as a decisive feature, are notmentioned and known to the patentees as properties essential to theapplication. The subject matter of U.S. Pat. No. 4,098,956 has thedisadvantage that the optical properties can be adapted to variousrequirements only by variation of the chemical composition. Thesenecessary changes in the chemical composition cause other necessaryproperties, for example, adhesiveness, to be lost. The authors report onthese disadvantages in another publication: Blickensderfer, R., D. K.Deardorff, R. L. Lincoln. 1977. Spectral reflectance of TiN_(x) andZrN_(x) films as selective solar absorbers. Solar Energy 19:429-432.,where problems with degradation in the case of such materials aredescribed.

Aside from numerous studies on TiN (see, for example, DE 3,210,420 or DE3,300,694) and titanium dioxide (see, for example, DE 3,116,677),titanium oxynitride (TiN_(x) O_(y)) was studied by Vogelzang, et al.(Vogelzang, E., J. Sjollema, H. J. Boer, J. Th. M. DeHosson. 1987.Optical absorption in TiN_(x) O_(y) compounds. J. Appl. Phys.61(9):4606-4611). In the cited study, the complex value dielectricconstant e(λ), as a function of wavelength λ in the 0.4 to 30 μm range,was published in addition to other measurement values. If thesepublished values and the Fresnel theory are used to calculate thedegrees of reflection and transmission, the calculations will not agreewith the results published by the authors in the same work. It musttherefore be assumed that an error has crept into the determination ofe(λ). Thus, the explanation of the optical and dielectric behavior inthis study is likewise inadequate, a practical application being, forthat reason, not possible.

Published in Offenlegungsschrift 3,640,086 A1 are compounds of titanium,nitrogen and carbon. It is required as a characteristic that the portionof oxygen be higher than that of nitrogen or carbon. But in this case,too, no attention is given to the void percentage.

The preparation of a material containing titanium, nitrogen and carbonis disclosed in DE 3,637,810 A1. It is known that dense layers developdue to the ion-plating used. It is therefore taken as a point ofdeparture that voids are lacking in these layers.

Materials with voids (or empty spaces) are described in the literaturerather frequently, for example, for thin layers consisting of TiN (see,for Example, Martin, P. J., R. P. Netterfield and W. G. Sainty. 1982.Optical properties of TiN_(x) produced by reactive evaporation andreactive ion-beam sputtering. Vacuum 32:359-362, or DE 4,207,368 A1),especially Schellinger, et al. on TiN_(x) O_(y) (Schellinger, H., M.Lazarov, H. Klank, R. Sizmann. 1993. Thermal and chemicalmetallic-dielectric transitions of TiN_(x) O_(y) -Cu absorber tandems.Proc. SPIE 2017, Optical Materials Technology for Energy Efficiency andSolar Energy Conversion XII). All authors thus far report on the mereexistence of voids. The quantification of the voids has not yet beenaccomplished.

Patent specification DT 2,216,432 C3 contains a report of titaniumdioxide with open porosity. The voids (pores) reported there have verylarge volumes.

Optical and electrical properties of materials can be classified intodielectric and metallic, the use of the materials being in this casedecisive. In the case of many applications, however, mixtures of the twoproperties are needed. In an absorber-reflector tandem (see, forexample, DE 2,639,388 C2 or DE 2,734,544 C2) neither a pure metal nor adielectric is able to deliver a selective absorption for solar rays.Semiconductors, with and without doping, meet such demands in part andare utilized in many applications. If one has in mind a selectiveabsorber, the fixed band gaps and the relatively flat absorption curve,typical for a semiconductor, are antithetical to highly selectiveproperties.

SUMMARY OF THE INVENTION

The purpose of the present invention is therefore to avoid the describeddisadvantages and produce a material with improved properties. A furtherobjective of the present invention is to make available a process forthe production of the invented material. A further goal consists in thedevelopment of a device utilizable in this process.

The problem is solved by the subject material which is composed of ametal from group IV B of the CAS periodic chart, nitrogen and oxygenhaving the formula MN_(x) O_(y) wherein M is a metal from group IV B,_(x) and _(y) range from about 0.1 to 1.7 and wherein 2 to 45% of thevolume is comprised of voids ranging from (0.5 nm)³ to about (100 nm)³in size and wherein the material is manufactured by a vacuum depositiontechnique.

The material according to the present invention comprises compounds ofone or more metals from group IV B of the periodic system, nitrogen andoxygen, in which case from 2 to 45%, preferably from 5 to 40%, verypreferably from 10 to 28% of the volume are formed by voids (emptyspaces) whose size lies in the range from (0.5 nm)³ to (100 nm)³. Theremaining volume of the material (98-55%, preferably 95-60%) exhibits acomposition of the group IVA metal of the periodic system to nitrogen tooxygen of 1:(0.1 to 1.7):(0.1 to 1.7), preferably 1:(0.25 to 1.5):(0.25to 1.5). The material has the formula MN_(x) O_(y), where "M" indicatesthe metal of group IV B of the periodic system and _(x) or _(y) thevalues 0.1 to 1.7. The above ratios refer to the particle number ormolar ratios. Regarding the size of the voids, it is preferred that thelatter occur in the lower range, i. e. preferably not larger than (15nm)³. The "remaining volume" of the material comprises preferably one ormore of the chemical compounds selected from MN_(x) (x=0.7 to 1.2),Magnelli phases of the M-O system (M_(n) O_(2n-1)), MO₂, M₂ N (withM=metal from group IV B of the periodic system) as well as approximately0-30%, preferably 0.5-5%, of carbon compounds of a metal of group IV Aof the periodic system. The range of important application options isexpanded by these preferably supplementarily contained compounds. Smallamounts of titanium carbides as impurities are not disturbing in thecase of many applications, but permit cheaper production. Thepossibility that the chemical phases present in the invented materialcan be available, preferably in crystalline or amorphous form, permitsvarious application fields to be covered, for example, in crystallineform as a diffusion barrier in the semiconductor industry or inamorphous form as a decorative layer. The metal from group IV B of theperiodic system is titanium, zirconium or hafnium or a mixture of two orthree metals, preferably titanium.

The invented material can be further described by the fact that, if p isthe average of the mass densities of the individual chemical compoundsof which the material is composed and p_(m) is the mass densities of thematerial including voids, the size ##EQU1## will lie in the range from0.02 to 0.5.

Furthermore it is preferred that the invented material exhibit voidswith a fractal size distribution. By means of the present specificationof the void type, the invented material is clearly delimited bymaterials whose reduced mass density is attributable to altered latticeconstants and high density of missing atoms in the lattice. The definedvoid portion and void distribution permit the invented material to beutilized as a standard in neutron scatter studies.

Further characteristic of the invented material is that the real part ofthe refractive index for the X-ray wavelength of 0.0709 nm willpreferably lie in the range from 0.9999984 to 0.9999973. The massdensity of the invented material lies preferably in the range from 3.7to 4.5 g/cm³, preferably from 3.8 to 4.2 g/cm³. By virtue of these theproperties, the invented material is also suitable for use as a standardin thin film density determinations.

A further property of the invented material is that the complex-valuedrefractive index for wavelengths in the 0.5 to 4.5 μm range points toneither typical metallic behavior nor to typical dielectric behavior.This makes the material very suitable as a radiation energy converter.Utilization for the conversion of radiation energy into heat demandsoptical properties in the infrared which are neither of a metallic nordielectric nature. Metallic properties can be described by a Drudetheory for the free movement of electrons in metal, while dielectricproperties are distinguished by the imaginary part of the refractiveindex. In the case of the invented material, electron-loss spectroscopic(EELS) measurements show a peak which can be interpreted as a plasmawavelength λ_(p) in the sense of the Drude theory for the free movementof electrons in metal, λ_(p) lying in the range from 1.1 to 0.1 μm. Thisplasma wavelength does not however correlate with typical metallicbehavior (describable by the Drude theory for the free movement ofelectrons in metal) of the optical constants.

The invented material is preferably available in the form of a powder orglass. This permits an application of the material in the volumetricabsorber field.

If use is made of titanium, zirconium or hafnium compounds, this expandsthe application range of the material to fields requiring hightemperature stability. Zirconium or hafnium compounds show higherthermal stability than titanium compounds, being furthermore resistantto diffusion processes.

The invented material can preferably be available as a thin layer whosecoating thickness is in the 3 nm to 3 mm range, preferably the 10 nm to2 mm range, and very preferably the range between 30 and 71 nm.

The thin layer thereby preferably exhibits a columnar micro- structure.This permits applications where the layer is to be porous or rough. Thisthin layer consisting of the invented material has a specific resistancein the range from 30 to 30,000 μΩ.cm, preferably from 100 to 6,000μΩ.cm, very preferably from 2,000 to 3,000 μΩ.cm. This propertyanticipates applications in the semiconductor industry in which,whenever a different specific resistance is needed, it should be easilypossible to alter the production process to meet these requirements inorder to keep costs down. The specific resistance can be adjusted by thechoice of the void portion without difficulty. Taking the specificresistance of the material without voids as a point of departure, thisproperty increases as voids are added. For example, in the case ofTiN₀.98 O₀.2, the specific resistance can lie at 70 μΩ×cm, if the voidshare is 3% and increases to values in the 650 μΩ range, if the voidshare is at 40%.

If still other supplementary compounds, like those listed in patentclaims 2 and 3, are present in the material, there is no need for themto occur in the same ratio at each level of the thin layer. This permitsuse as a gradient coating, for example, in the case of selectivecoatings it is desired to alter the optical properties with the layerthickness. This can be easily accomplished here by variation of thechemical compounds or by changing the share of voids. By preference, theportion of voids changes with the depth of the thin layer. It ispreferred that the uppermost 0 to 50% of the thin layer, measured at thetotal thickness, consist of TiO₂, ZrO₂ or HfO₂.

The material is thereby suitable for applications in which the uppermostlayers are to have electrical properties, for example, in the case ofinsulators.

The invented material can be applied preferably as a thin coating to ametallic substrate consisting of molybdenum, silver, gold, copper,aluminum, tungsten, nickel, chromium, zirconium, titanium, hafnium,tantalum, niobium, vanadium, iron and their alloys. The metallicsubstrate can be applied in turn to any other solid carrier. Themetallic substrate is preferably one produced by a rolling or pouringprocess and contains impurities. The invented material, formed as a thincoating, is preferably applied to a rough substrate, whose roughness ischaracterized by a statistical distribution of deviations from anaverage level, the standard deviation of this distribution lying in the0-1,500 nm range, preferably 40-120 nm. The roughness makes possiblebetter absorption in the case of short wavelengths and therefore permitsits use as an absorber-reflector tandem.

The material per the invention, formed as a thin layer, can be coated byan additional thin layer consisting of one or more oxides, preferablySiO₂, ZrO₂, HfO₂, Al₂ O₃, Y₂ O₃. With this additional layer, which ispreferably thinner than 60 nm, the material can be passivated,prolonging its useful life. A layer system, consisting of the inventedmaterial with preferably 1-45 oxide layers, can be employed as anantireflective filter. The oxides and coating depths of the system arethereby chosen by means of an algorithm, so that the reflection for aspecific wavelength range will be particularly high. Appropriatealgorithms can be taken from the pertinent literature (for example,Eisenhammer, T., M. Lazarov, N. Leutbacher, U. Schoffel and R. Sizmann.1993. "Optimization of interference filters with genetic algorithms,applied to silver-based heat mirrors". Applied Optics. 32). Such acoating system, to which the invented material is applied, can have areflection-reducing effect, while permitting better absorption ofspecific wavelengths. It is preferred that the sum of the products ofthe coating thickness of each antireflective layer, multiplied by therefractive index (measured in the visible wavelength range) of theemployed material of the additional layer, be in the range from 20-80nm, preferably from 80-110 nm.

As already mentioned, the incorporation of voids sets a balance betweenvarious competing properties, for example, the electrical and metallicones. In addition to the optical properties, the electrical propertiescan also be correspondingly altered. A specific resistance of preferably3.500 μΩ×cm is brought about by a 20-25% (vol.-%) share of voids in thematerial. Only the control of voids permits the controlled variation ofspecific resistance and explains the influence of the plasma frequenciesupon the optical properties. Only this permits controlled designing ofthe properties of this material important for certain applications, forexample, as selective absorbers.

The invented materials with adjustable properties, which are also bothelectrically and temperature resistant, are useful in various branchesof industry:

In solar energy: If the invented material, with a void portion ofpreferably 22-26 vol.-%, is coated onto prefer-ably copper, molybdenumor aluminum by means of a coating process to a thickness of preferably40-70 nm, a selective absorber results. The latter is able to convertincident solar radiation into heat with temperatures up to 400° C.,without the need to concentrate the radiation. In addition, the materialproperties are adapted by controlling the chemical compositions and theportion of voids for optimal yields from the solar radiation as afunction of the temperature desired for the heat energy, the weather andthe concentration. For solar energy applications, the material ispreferably applied as a thin layer to a metallic substrate (metalsubstrate) having any geometry, and the coating thickness is preferablychosen in the 40-80 nm range, so that the combination of thin layer andmetallic substrate will absorb wavelengths as selective absorbers,concerting the incoming radiation from the sun into heat energy.Preferred thereby is the absorption of wavelengths in the 0.3 to 1.5 μmrange. For the application in solar energy, the invented material has avoid share in terms of volume of preferably 20-30%, a layer thickness of40-70 nm, the metal substrate used being preferably copper or aluminum.In addition, an antireflective layer consisting of SiO₂ with a thicknessof 70-120 nm, preferably from 85 to 100 nm, can be used. When used withsolar energy, the radiation energy is absorbed in the material and thematerial thereby warmed, the heat energy being drawn off by a connectionto a heat carrier. The heat carrier can thereby be one or more phases ofwater. The absorber can be built into any type of solar radiationcollector.

In the semiconductor industry: It is known that silver and gold diffusethrough thin layers consisting of TiN. These diffusion rates are smalland poorly controllable. With the invented material the diffusion ratecan be significantly increased and the electrical properties of thelayer set within wide limits at the same time. In particular, thespecific resistance can be made large (preferably 1,000-30,000 μΩ×cm).It is thus possible to produce circuit board traces of silver and goldby tempering.

As a coating for the vanes of a light mill: If a thin, heat-insulatingslab, preferably of mica or an aerogel, is coated with copper, silver oraluminum of a thickness of approximately 200 to 1,000 nm and is thencoated with the invented material with a preferred thickness of 40-150nm to produce a selective radiation converter, this slab will then bevery suitable for use as a vane in a light mill.

As a decorative layer: The invented material is suitable for usepreferably as a decorative layer, if the material is applied in athickness between 15 to 400 nm, preferably 30-150 nm, to a substrate, avisual impression of color will be produced by the interference effectsof this combination. The material and the substrate can be therebycovered with a thin (approximately 60-120 nm), preferably partiallytransparent layer.

In powerplant technology: The invented material is suitable furthersuitable as a selective radiation emitter for the conversion of heatenergy into electricity, the material being warmed and, as a selectiveradiation transmitter, liberating heat which is converted into currentby means of a photocell. A coating of the invented material to a depthof 50-500 nm, preferably approximately 100-200 nm, on a substrate(preferably molybdenum), the material having a void content of 7-20% byvolume, is preferred in the power industry as a selective emitter.Because the invented material is temperature-stable, the emitter can beheated to temperatures above 900° C.

In medicine: The interchange between dielectric and metallic propertiesis on a scale in the nm-range. It is known that metals, for example,silver, have an antimicrobial effect, though bacteria adhere to metalseasily and form a film, they die there. New germs may also be presentthere, which are not killed, because they have no contact with themetal. Dielectric materials have germ-repellent properties. Because theinvented material is in possession of both antimicrobial (metallic) aswell as germ-repellent (dielectric) properties, bacteria are killed, butdo not remain adherent. The antimicrobial effect remains intact.

This broad range of applications results from control of the physicalproperties via the voids. This control can be predicted simply by meansof the effective media theory according to Bruggeman, which views thematerial as a mixture of voids and the participating phases. It is asignificant advantage of the invention that the desired optical andelectrical properties are not modulated by the chemical compositionalone, but in addition by the voids. Important properties, such asadhesiveness, temperature stability, corrosion resistance, etc., arethereby able to remain intact, which are essentially determined by thechemistry.

Further advantages of the invention are that

the metals of group IV B of the periodic system, nitrogen and oxygen, aswell as the compounds produced from them, are not poisonous, and

the compounds of titanium, zirconium or hafnium with nitrogen and oxygenare temperature-stable, resistant (hard) and light in comparison tometals like iron or copper.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described with reference to FIGS. 1 through 9.

FIG. 1 shows the imaginary part of the refractive index at 10 μm as afunction of the void percentage for TiN_(x) O_(y) (crosses) and ZrN_(x)O_(y) (triangles) (with x=0.7-0.9; y=0.3-0.6).

FIG. 2 shows the degree of solar absorption of a 55 nm thick TiN_(x)O_(y) -Cu absorber as a function of the void percentage (with x=0.7-0.9;y=0.3-0.6).

FIG. 3 shows the degree of thermal emission at 250° C. of a 55 nm thickTiN_(x) O_(y) absorber as a function of the void percentage (withx=0.7-0.9; y=0.3-0.6).

FIG. 4 shows the element composition relative to titanium relative totitanium as a function of the partial pres-sure of oxygen in the coatingin the case of TiN_(x) O_(y) (with x=0.7-0.9; y=0.3-0.6).

FIG. 5 shows the quotients of coating mass density to bulk density as afunction of the void share in TiN_(x) O_(y) (crosses) and ZrN_(x) O_(y)(triangles) (with x=0.7-0.9; y=0.3-0.6).

FIG. 6 shows the real portion of the refractive index as a function ofthe wavelength at various void percentages in TiN_(x) O_(y) (withx=0.7-0.9; y=0.3-0.6).

FIG. 7 shows the imaginary part of the refractive index as a function ofthe wavelength for various portions of voids in the case of TiN_(x)O_(y) (with x=0.7-0.9; y=0.3-0.6).

FIG. 8 shows a section through a selective solar absorber in which theinvented material is used.

FIG. 9 shows a section through the device for producing the inventedmaterial.

DETAILED DESCRIPTION OF THE INVENTION

Furthermore, the goal of the present invention is achieved by a processfor the reactive vacuum deposition or activated vacuum deposition. Perthe invention, an oxide, nitride or carbide compound arises duringdeposition of the metal from group IV B of the periodic system onto asubstrate by maintaining a gas atmosphere containing at least one of thegas types N₂, O₂, CH₄ and/or noble gases. The condensation of the metalparticles on a heatable substrate is thereby controlled by means the gaspressure p_(tot), the evaporation rate r, the substrate temperatureT_(sub) and by the distance 1 between metal source and substrate in sucha way that the volume share of voids amounts to from 2 to 45% by volume,their magnitude lying in the range from (0.5 nm)³ to (100 nm)³. Theproduction parameters are chosen as follows:

T=20° to 400° C.,

1=0.01 to 1.5 m

the partial pressure ratio of the gases N₂ and O₂ : (p_(N2) /p_(O2))=1to 2,000,

p_(tot) =2×10⁻⁵ hPa-4×10⁻² hPa and

r=0.01 to 60 nanometers/s.

In the case of the production parameters it is necessary, to set them insuch a way that the void content can be predicted. This can beaccomplished by means of the following process: for substratetemperatures in the range of preferably from 100° to 220° C. and adistance 1 between the evaporator source and the substrate in the rangeof preferably from 0.5 to 1.2 m, the following holds true:

A volume percentage of 34% of voids is achieved, if ##EQU2## and thetotal gas pressure p_(tot) lies in the range of from 2×¹⁰ -3 to 2×10⁻²hPa.

A volume share of 20% of voids is achieved, if the choice is made in the##EQU3## range. Volume percentages between 20 and 34% can be specifiedby selection of the magnitude K according to the following equation:##EQU4##

There is thus the possibility of achieving the desired portion of voidsin the invented material both with the rate r, with the total pressurep_(tot) and with the distance 1.

Analogously, it is possible to control the volume percentage of voids inthe layer for substrate temperatures in the range of preferably from250° to 400° C. and distance 1 in the range of preferably from 0.5 to1.2 m in the following manner:

A volume share of, for example, 40% voids is achieved if ##EQU5## andp_(tot) lies in the range of 2×10⁻² hPa to 4×10⁻² hPa. If K is chosen inthe range of ##EQU6## the volume percentage of voids is 20%. To achievevalues between 20 and 40%, K must be chosen according to the equation:##EQU7## Volume percentages lying in between can of course be determinedby linear interpolation. Small volume shares of voids (2-20%) areachieved at small rates 0.01-0.1 nm/s and low gas pressures of 10⁻⁴mBar. Very large void percentages (>40%) are produced at high total gaspressures >4×10⁻² mBar. At these gas pressures, the material can bepresent as a loose bond. Per the invention, the coating is applied to asubstrate preferably of molybdenum, silver, gold, copper, aluminum,tungsten, nickel, zirconium, hafnium, tantalum, niobium, vanadium, ironor alloys of the same. To produce the material as a block, without asubstrate, the following two methods are suitable:

The (PVD) deposition takes place on NaCl, KBr or on other salts in anythickness. The salt is then dissolved in water, and invented materialremains behind.

The deposition is effected onto thin metal with a low melting point,such as copper, aluminum, tin, zinc or brass. The material and thesubstrate (base) are then heated under high vacuum (10⁻¹⁰), and ofcourse at temperatures near the melting point of the metal, so that themetallic substrate evaporates. Remaining behind is the inventedmaterial.

The coating thickness is optional, preferably from 30 to 120 nm. Bypreference, the gas atmosphere can also contain H₂ O and volatilecompounds of carbon. The production process can thereby be arranged morecheaply. It is conceivable in many cases to replace oxygen entirely withwater, or to admit air.

Moreover, the goal of the present invention is achieved by a device forthe vacuum deposition of thin layers of the invented material. In thatcase, in a vacuum deposition chamber, a metal from group IV B of theperiodic system is deposited by means of evaporation on a substratelocated in the apparatus from 0.01 to 1.5 m from the evaporationcrucible. A gas atmosphere is maintained via one or more gas meteringvalves or gas flow meters and measurement as well as regulation of thepartial pressures with a mass spectrometer. The gas atmosphere containsat least one of the gas types N₂, O₂, CH₄ and noble gases. The substratetemperature is regulated in the 20°-400° C. range via a regulator,preferably a PiD regulator. The evaporation rate is measured with aquartz oscillator and its signal controls the output of the evaporatorby means of a regulator, preferably a PiD regulator. The evaporationdesired is set. The coating parameters indicated above are achieved withthe device. In addition, the total gas pressure is determined with atotal gas pressure meter. Utilized for evaporation is an electron-beamevaporator and/or a resistance evaporator and/or an inductiveevaporator. The invented device becomes less expensive when a resistanceor inductive evaporator is used. The substrate is heated to thenecessary substrate temperature from 20° to 400° C. preferably by meansof radiation heating and regulated. Also suitable is inductive heatingor electrical resistance heating.

The evaporation of the metal takes place preferably in a separateevacuatable chamber, and this chamber is connected by means of a shutterwith a chamber containing the gas atmosphere and the substrate. Thisexecution variant permit a higher overall pressure, without reducing theworking life of the evaporator.

The gas atmosphere mixture is preferably controlled via separate gasflow meters or by means of a mass spectrometer. Suitable for measuringthe size of p_(tot) is, for example, a friction manometer or a baratron.Gradient layers are also produced by the invented device. In theselayers, the composition changes with the coating depth. This can becontrolled with the composition of the gases introduced. An increase ofN₂ produces coatings containing more nitrogen. The gas composition canbe regulated via the inflow or the measurement of the partial pressures.If the friction manometer is employed, it is possible to deliverreproducible coating properties with the invented device.

If the substrate is a strip or a foil formed according to the cos^(II)-characteristic of the evaporator (with n=1 to 7) of the evaporator, sothat it is adapted to the evaporator characteristic of the evaporator, auniform coating over the entire surface is assured.

By preference, the coating chamber is connected to one or more furthercoating chambers by a separately evacuatable vacuum line, the substratebeing passed from one chamber to another without breaking the vacuum andsubmitted to a separate coating process. Multilayer systems are theresult.

EXAMPLE 1

In a high vacuum installation, titanium and zirconium are evaporated bymeans of an electron-beam evaporator in gas mixture of nitrogen andoxygen. The nitrogen partial pressure was 2.5 to 9.5×10⁻⁴ mBar, and theoxygen partial pressure was varied in the range from 1×10⁻⁸ mBar to8×10⁻⁵ mBar. Coated were 2 mm thick copper disks and 1 mm thick glassdisks. This substrate was held at 170° C. during the process. A plasmadischarge was ignited in the recipients by means of a surface electrode.This increases the readiness for the formation of TiN and TiO, or ZrNand ZrO, in the layer. Produced for purposes of analysis were samples ofvarious layer thicknesses (30 to 120 nanometers) and void percentages(5-32% by volume). The partial pressure ratio of N₂ to O₂ was therebyheld at 35, and the distance of the substrate from the evaporator was0.8 m. The void percentage is controlled by means of the evaporationrate, which assumed the following values: 0.06 nm/s for small voidpercentages and up to 0.2 nm/s for high percentages of voids.

The crystalline phases TiN and TiO, or ZrN and ZrO, are identified bymeans of X-ray reflectometry. The element composition was measured viaelastic record detection (ERD). Layer thickness and layer density weredetermined by means of grazing incidence X-ray reflectometry (GIXR). Theportion of voids and their size distribution was determined bymeasurement of the scattered X-ray radiation with grazing incidence.

It was apparent that the mass density of the layer relative to the TiOor TiN mass was reduced by the percentage filled with voids. Forzirconium, there were deviations of from 3 to 5% from this rule. Thedegree of solar absorption α_(sol) was determined from measurements ofthe degree of aimed hemispherical reflection ρ(λ) according to ##EQU8##Here AM 15 (λ) is the standard solar spectrum AM 1.5 and lambda thewavelength of the radiation. The degree of thermal emission was measuredcalorimetrically at temperatures from 150° to 400° C.

The optical constants were determined from reflection and transmissionmeasurements with generally known graphical methods.

The results are presented in FIGS. 1 through 7. These are described herein detail.

FIG. 1 shows the imaginary part of the refractive index at 10 μm as afunction of the portion of voids for TiN_(x) O_(y) (crosses) and ZrN_(x)O_(y) (triangles). The imaginary part without voids is high, a typicalproperty of metals. A 20% to 25% portion of voids produces a mix-ture ofmetallic and dielectric behaviors. In both examples, it is apparent thata 20-30% portion of voids can produce a reduction of the imaginary partof the refractive index to moderate values. This means in the case ofapplications as a solar absorber that the degree of thermal emission canbe kept low. The refractive index can be determined ellipsometrically orby measurement of the degrees of reflection and transmission. Thepercentage of voids and their size was determined by X-ray scatter orneutron scatter.

FIG. 2 shows the degree of absorption of a 55 nanometer thick TiN_(x)O_(y) -Cu absorber as a function of the percentage of voids. Bymeasurement of the degree of reflection of the absorber and folding withthe spectrum of the solar radiation incident to the earth, adetermination was made of the share of absorbed energy, the degree ofsolar absorption. A maximal degree of absorption of the incident solarradiation results from a material whose void percentage amounts to27.5%.

FIG. 3 shows the degree of thermal emission at 250° C. of a 55 nanometerthick TiN_(x) O_(y) -Cu absorber as a function of the void share. Thedegree of thermal emission decreases with an increasing share of voids,which can be explained by the decrease in metallic properties. Tomeasure the degree of thermal emission, the sample must be placed undera vacuum at the temperature of measurement, in this example, 250° C. Itis achieved by means of a suitable structure that the sample loses heatonly by means of radiation. The degree of emission is calculated fromthe energy balance.

FIG. 4 shows the elemental composition relative to titanium as afunction of the partial pressure of oxygen in the layer for TiN_(x)O_(y). The nitrogen to oxygen ratio was kept in the invented device forproducing the invented material with the range from 1 to 2,000. Therebyresulting from a low partial pressure of oxygen were the chemicalproperties needed for applications as a selective absorber of solarenergy, for example, high adhesiveness.

FIG. 5 shows the quotient of the layer mass density to bulk density as afunction of the void percentage in the case of TiN_(x) O_(y) (crosses)and ZrN_(x) Y_(y) (triangles). It is evident that the mass density isgoverned by the void percentage.

FIG. 6 shows the real part of the refractive index as a function of thewavelength for various void percentages in the case of TiN_(x) O_(y)coatings. With a void share of 18% by volume, the real part of therefractive index still shows metallic properties and rises withwavelength. With a 22% by volume share, neither metallic nor dielectricproperties dominate, and at 32% by volume, the material is essentiallydielectric.

FIG. 7 shows the imaginary part of the refractive index as a function ofthe wavelength for various void percentages in TiN_(x) O_(y) coatings.With a void portion of 18% by volume, the imaginary part of therefractive index still shows metallic proper-ties and rises withwavelength. With a 22% by volume share, neither metallic nor dielectricproperties dominate, and at 32% by volume the material is dielectricwithin broad wavelength ranges.

FIG. 8: An application of the invented material is shown in Fi. 8.Presented in FIG. 8 is a section through a selective solar absorber, inwhich the invented material (2) is used. On a highly reflectivesubstrate (1), copper, a 55 nanometer thick coating of the inventedmaterial (2) is applied, and the latter is covered in turn with a 92nanometer thick antireflective layer consisting of SiO₂ (3). Theantireflective layer increases the degree of solar absorption from 0.8to 0.94. The invented material (2) is one characterized by a voidcontent of 27.5% by volume and a titanium:oxygen:nitrogen ratio of1:0.92:0.35.

FIG. 9 shows a section through the invented production apparatus. Acopper strip (2) is passed over an electron beam evaporator (1). This iskept in a curved shape by rollers (3) in such a way that the coating isuniform. The curve follows the characteristic of the evaporator whichcan differ from that of a Lambert radiator. Whereas the characteristicof a Lambert radiator can be described by the "cosine¹ law", amodification of the law must be considered in the case of an electronbeam evaporator, that is to say, a "cosine^(n) " characteristic isfollowed with n in the range of from 1 to 7.

We claim:
 1. A process for the production of thin layers of acomposition of a metal M from Group IV B of the periodic system,nitrogen and oxygen, having a formula of MN_(x) O_(y) wherein _(x) and_(y) each ranges from about 0.1 to about 1.7, by means of reactivevacuum deposition or activated reactive vacuum deposition, wherein,during the deposition of the metal from Group IV B of the periodicsystem, maintaining a gas atmosphere comprising N₂ and O₂ gas, andcontrolling deposition of evaporated metal particles onto a heatablesubstrate via total gas pressure p_(tot), evaporation rate r, substratetemperature T_(sub) and distance 1 between a metal evaporation sourceand a substrate, in which case these parameters lie in the rangesT_(sub)=20° to 400° C., 1=0.01 to 1.5 m, the partial pressure ratio of thegases N₂ and O₂ ; (p_(N2) /p_(O2))=1 to 2,000, p_(tot) =2×10⁻⁵hPa-4×10⁻² hPa, r=0.01 to 60 nm/s,so that layers with a volume share ofvoids of from 2 to 45% arises, whose size lies in the range from (0.5nm)³ to (100 nm)³.
 2. Process according to claim 1, wherein the layer isapplied to a metallic substrate selected from the group consisting ofmolybdenum, silver, gold, copper, aluminum, tungsten, nickel, chromium,zirconium, titanium, hafnium, tantalum, niobium, vanadium, iron andtheir alloys.
 3. Process according to claim 1, wherein the layerthickness is from 30 to 120 nm.
 4. Process according to claim 2, whereinthe layer thickness is from 30 to 120 nm.
 5. Process according to claim1, wherein the gas atmosphere comprises H₂ O and volatile compounds ofcarbon.
 6. Process according to claim 2, wherein the gas atmospherecomprises H₂ O and volatile compounds of carbon.
 7. A process accordingto claim 1, wherein the gas atmosphere further comprises at least onegas selected from the group consisting of CH₄ and noble gases.
 8. Aprocess for the production of thin layers on a substrate of materialcomprising chemical compounds of one or more metals (M) of group IV B ofthe periodic system, nitrogen (N) and oxygen (O), said processcomprising:depositing metal from Group IV B of the periodic system;maintaining a gas atmosphere during said depositing wherein theatmosphere comprises at least one gas selected from the group consistingof N₂, O₂, CH₄, and noble gases, controlling the total gas pressurep_(tot) between about 2×10⁻⁵ h Pa and about 4×10⁻² h Pa, controlling theevaporation rate r between about 0.01 and about 60 nm/s, controlling thesubstrate temperature T_(sub) between about 20° and about 400° C.,controlling the distance 1 between a metal evaporation source and thesubstrate between about 0.01 and about 1.5 m, wherein the layerscomprise a volume share of voids of from about 2 to about 45%, whereinthe size of the voids range from about (0.5 nm)³ to about (100 nm)³. 9.A process according to claim 8, wherein said substrate comprises amaterial selected from the group consisting of molybdenum, silver, gold,copper, aluminum, tungsten, nickel, chromium, zirconium, titanium,hafnium, tantalum, niobium, vanadium, iron and alloys of thesematerials.
 10. A process according to claim 8, wherein the thickness ofsaid layer is from about 30 nm to about 120 nm.
 11. A process accordingto claim 8, wherein the gas atmosphere in said maintaining step furthercomprises H₂ O and volatile compounds of carbon.
 12. A process accordingto claim 8, wherein said depositing comprises reactive vacuumdeposition.
 13. A process according to claim 8, wherein said depositingcomprises activated reactive vacuum deposition.
 14. A process as inclaim 8, further comprising coating the layers with at least oneadditional layer of oxide.
 15. A process as in claim 14, wherein theadditional layer of said coating the layers comprises an oxide selectedfrom the group consisting of SiO₂, ZrO₂, HfO₂, Al₂ O₃, and Y₂ O₃.